The invention pertains to apparatus for making electrical connections along a well conduit, although certain features of the invention are also applicable to electrical connection apparatus used in other contexts, and other features of the invention are applicable to the mounting of various other types of devices or systems in well conduits.
It is often necessary, for one reason or another, to transmit an electric current along the length of a well conduit. Typically, such current is transmitted along a drill string during drilling of the well. For example, there may be electronic apparatus located near the drill bit for taking readings of various parameters such as downhole physical and/or chemical conditions and/or directional drilling information. Such devices produce signals which are electrically transmitted along the drill string to the top of the well for communication to the operator, while power for operating these devices and/or electrical control signals are transmitted downwardly along the drill string.
Various systems currently available for providing such electrical communication along a well conduit each suffer from respective disadvantages. Some such systems employ more or less conventional pin and socket type electrical couplers mounted in centralized positions within the central bore of the drill string. See U.S. Pat. No. 4,051,456. The major disadvantage of these systems is that they prevent running of wire line tools through the drill string.
Other systems involve electrical apparatus built into the sections of drill stem themselves. For example, systems disclosed in U.S. Pat. No. 3,696,332, No. 3,518,608 and No. 3,879,097 employ electrical contacts embedded in the seal shoulders or pins and boxes of the drill stems and electric conductors extending through the side walls of such stems. Such systems minimize obstruction of the bore of the drill string. Also, because the contacts are located on the seal shoulders or threaded portions of the drill stems, they are automatically connected as the string is made up, and furthermore, are fairly well protected against contact with the drilling fluid. However, a major disadvantage of these systems is that they are expensive, requiring special manufacture of the drill stem sections to be used in the operations in question.
Other systems ae designed to be installed in standard pipe sections, e.g. U.S. Pat. No. 4,012,092, but require special apparatus for such installation.
Still other systems have attempted to provide for field installation. However, they still require at least some special machining of the drill stems to be used.
Another problem which arises with electrical couplers used downhole and/or in deep underwater environments is that of adequately protecting such contacts against exposure to the fluids in those environments. In downhole applications, it is particularly important to avoid exposure of the contacts to the drilling fluid for several reasons. Probably the most important reason is that typical drilling fluids themselves have conductive properties. Another is that a clean contact will make a better connection with its mate. Finally, the drilling fluid, salt water, and/or other fluids encountered in such environments may be corrosive or otherwise harmful to preferred contact materials, particularly at the high temperatures of those environments.